This application relates to a composite coating that is designed to resist erosion in a gas turbine engine section.
Gas turbine engines are known and, typically, include a compressor which compresses air and delivers it into a combustion section. The air is mixed with fuel and ignited in the combustion section and products of the combustion pass downstream over turbine rotors.
Recently, the efficiency of the gas turbine engine is a source of much design concentration. One aspect leading to greater efficiency is to ensure that the bulk of the energy delivered to the compressor section is effectively used to compress the air delivered into the combustion section. To this end, clearances between rotating compressor blades and an outer seal are maintained as tight as possible.
However, recently aircraft are utilized in more challenging environments where particulate erosion can increase these clearances. As an example, aircraft are often used in environments in which particulate material is mixed with air. This becomes particularly challenging in helicopter mounted gas turbine engines as they are even more often utilized in dusty environments.
The sand impacts the coating layers at a low angle and is abrasive.
Thus, it is desirable to form abrasion resistant coatings. However, it also sometimes occurs that the blade length can increase, such as during a surge condition, and contact the coating. Under such conditions, it would not be desirable for the coating to be too strong as this can damage the blade.